Field of the Invention
This invention relates to AC electric energy meters and more particularly to an AC electric energy meter capable of driving a mechanical register based on a pulse signal output by an electronic AC electrical energy measuring circuit.
Devices for AC electric energy measurement are extensively used by producers of electric energy for measuring consumption by individual energy users. Typically, such meters are watthour meters which are used for indicating energy consumption in kilowatthours. Many watthour meters which are currently in use, are induction type watthour meters which have a rotating disk and which provide a high degree of reliability and accuracy. Further, these induction type watthour meters are available at reasonable cost and are capable of outdoor operation under widely varying extremes of temperature and other ambient conditions.
Recently, electronic AC electrical energy measuring circuits, or solid state watt meter circuits, have been developed, which do not employ a rotating disk but which instead produce a pulse signal, wherein each output pulse of the pulse signal is equivalent to a single rotation of the disk in a conventional induction type watthour meter. This type of electronic watt meter is described in U.S. Pat. No. 4,182,983 to Heinrich et al., assigned to the assignee of the subject application. These electronic watt meters are more accurate and tamper-resistant than the above-described rotating disk arrangement. However, with the electronic watt meter, it is necessary to count the pulses and to store the pulses in a non-volatile manner since the incremental count of the pulses over a period of time is proportional to the amount of energy consumed. While the pulses can be counted, stored and displayed in a totally electronic manner, costs and durability considerations have led to a desire to employ a mechanical register of the type which is currently used in conventional induction type watthour meters. Further, in view of the fact that watthour meters are not replaced for many years, the use of a mechanical register for both induction type watthour meters and electronic watthour meters has a number of advantages in that a uniform display is provided, which can be easily and accurately read for billing purposes.
While the need for an AC electric energy meter which combines an electronic AC electrical energy measuring circuit and a mechanical register exists, thus far there has not been an economical and accurate solution to the problem of driving the mechanical register based on the pulse signal output by the electronic AC electrical energy measuring circuit. While it would be desirable to be able to drive the mechanical register using the AC electric energy source, this typically requires the use of an expensive inverter circuit and/or expensive and bulky power supply transformers. Therefore, there remains a need in the art for an AC electric energy meter which employs the pulse signal output by an electronic AC electrical energy measuring circuit in conjunction with a conventional mechanical register to provide the desired non-volatile watthour display.